Control system



Nov. 23, 1965 R. N. FRANCIS 3,219,051

CONTROL SYSTEM Filed June 25, 1962 3a ABSORBENT 49 4a SURGE +S ABSORBER INVENTOR.

R. N. FRANCIS A TTORNEYS United States Patent 3,219,051 CONTROL SYSTEM Robert N. Francis, Bartlesville, 0kla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed June 25, 1962, Ser. No. 204,703 2 Claims. (Cl. 137-118) This invention relates to controlling the flow of liquid from a vessel in response to changes in liquid level within the vessel. In another aspect it relates to the control of centrifugal pumps.

In the petroleum refining industry, it is common practice to recover natural gasoline from gaseous hydrocarbon streams. This is usually accomplished by dissolving the gasoline components in an absorption oil in a contacting vessel. In some operations, the resulting rich oil obtained from a relatively low pressure absorber i passed to a second absorber which is operated at a high pressure. The transfer of the oil from the low pressure absorber to the high pressure absorber normally is accomplished by use of a centrifugal pump. However, the resulting pressure drop in the pump often results in flashing of some of the light hydrocarbons from the absorption oil. These flashed hydrocarbons can create a gas pocket in the pump which prevents the passage of additional liquid by the pump.

The present invention provides a solution to this problem. A first control valve is disposed at a point down stream from the pump and is regulated in response to a measurement of the liquid level in the low pressure absorber. Under normal operating conditions, this provides sufficient control of the flow of oil. A second conduit, having a second control valvetherein, communicates with the low pressure absorber to vent a portion of the rich oil if the measured liquid level in the absorber should exceed a preselected value even after the first control valve is opened fully. This second valve is also regulated by the liquid level controller. A third conduit, having a third control valve therein, communicates directly with the interior of the centrifugal pump to vent gases therefrom. This third control valve is opened in response to the liquid level controller if flows through the first conduits are not suflicient to reduce the liquid level to the desired value. 7

Accordingly, it is an object of this invention to provide apparatus for regulating the rate at which liquid is removed from a vessel.

Another object is to provide a system for controlling the How of oil from a first absorber to a second absorber.

A further object is to provide apparatus for venting a centrifugal pump when pockets of gas accumulate therein which prevent the normal flow of liquid through the pump.

Other objects, advantages and features of the invention should become apparent from the following description, taken in conjunction with the accompanying drawing which is a schematic representation of an embodiment of the control system of this invention.

Referring'now to the drawing in detail, there are shown first and second absorbers 10 and 11. A first stream of gaseous hydrocarbons at relatively low pressure is introduced into absorber 10 through a conduit 12. It is generally desired that this gas be introduced at a relatively constant rate. Lean absorption oil is introduced into an intermediate region of absorber 10 through a conduit 13 and into an upper region of the absorber through a conduit 14. Conduits 13 and 14 receive le-an oil from sources described hereinafter. This lean oil flows downwardly through absorber 10 and contacts the gases which rise through the absorber. The natural gasoline components in the gaseous stream are absorbed by the oil "ice and are removed from the lower region of the absorber through a conduit 15 which communicates with the inlet of'a centrifugal pump 16. Gases which are not absorbed are removed from the top of the absorber through a conduit 17.

A conduit 18, which has a cooler 19 and a control valve 20 therein, communicates between the outlet of pump 16 and an intermediate region of absorber 11. A second gaseous stream at a relatively high pressure is introduced into the lower region of absorber 11 through a conduit 21. Additional lean absorption oil is introduced into the upper region of absorber 11 through a conduit 22. Gases which are not absorbed are removed from the top of absorber 11 through a conduit 26. The resulting rich oil is removed from the lower region of absorber 11 through a' conduit 24 which communicates with a first flash chamber 25. Conduit 24 has a valve 27 therein which is regulated by a liquid level controller 23 on absorber 11. A portion of the absorbed hydro carbons is removed from the rich oil in flash chamber 25 and returned to absorber 10 through a conduit 28 which communicates with conduit 12. A pressure controller 29 adjusts a control valve 30 in conduit 28 to maintain a predetermined pressure in fl-ash chamber 25.

The remaining rich oil is removed from the lower region of flash chamber 25 through a conduit 31. which communicates with a second flash chamber 32. A liquid level controller 33 adjusts a valve 34 in conduit 31 to maintain a predetermined level of rich oil in chamber 25. Gases which are flashed from the oil in chamber 32 are removed through a conduit 35. A pressure controller 36 adjusts a valve 37' in conduit to maintain a predetermined pressure in chamber 32. The rich oil remaining in chamber 32 is removed through a conduit 37 which communicates with the inlet of a stripper 38. A liquid level controller 39 adjusts a valve 40 in conduit 37 to maintain a predetermined liquid level in chamber 32. A heat exchanger 41 is disposed in conduit 37.

Heat is supplied to the lower region of stripper 38 by means of a steam coil 42 or other appropriate heat source.

I The gases stripped from the oil are removed from the top of stripper 38 through a conduit 43. The resulting lean absorption oil is removed from the bottom of stripper 38 through a conduit 44 which communicates through heat exchanger 41 and a cooler 45 with a surge tank 46. Additional fresh absorbent is introduced into tank 46, as required, through a conduit 47. Conduit 48, which has a pump 49 therein, communicates between surge tank 46 and conduits 14 and 22. A predetermined flow rate is maintained through conduit 14 by a flow controller 50 which adjusts a valve 51, and a predetermined flow rate is maintained through conduit 22 by a flow controller 52 which adjusts a valve 53. Conduit 13 communicates with conduit 37 downstream from valve 40. The oil returned through conduit 13 is thus only partially stripped. A cooler 54 is disposed in conduit 13. A predetermined flow rate is maintained through conduit 13 by means of a flow controller 55 which adjusts a valve 56.

The rich oil removed from absorber 10 through conduit 15 contains some relatively light hydrocarbons which can flash within pump 16. This is avoided to some extent by adding a preselected amount of relatively lean oil to the rich oil removed from absorber 10. To this end, a conduit 58 communicates between conduit 13 and conduit 15. The flow through conduit 58 is maintained at a predetermined rate by a flow controller 59 which adjusts a valve 60.

Control valve 20 is regulated by means of a liquid level controller 61 which is associated with absorber 10. In normal operation, controller 61 opens valve 20 when the liquid level in the absorber tends to rise above a preselected value. However, in many operations, the liquid level in absorber often continues to rise even after valve 20 is opened fully. When this occurs, the increased output signal from controller 61 serves to open a second control valve 62 which is disposed in a conduit 63. Conduit 63 is connected between conduit and conduit 31 so that a portion of the rich oil from absorber 10 bypasses pump 16 when the liquid level in the absorber rises above a preselected value. If a gas pocket should develop within pump 16, even the opening of valve 62 may not be sufficient to reduce the liquid level in the absorber to a desired value. When this occurs, the increased output signal from controller 61 is applied to a control valve 65 which regulates the passage of air at a predetermined pressure from a conduit 66 to a control valve 68. Valve 68 is disposed in a conduit 69 which communicates between the interior of pump 16 and conduit 63. Under normal operation, valve 65 is closed. When the liquid level in absorber 10 exceeds a preselected height, valve 65 transfers the air pressure to value 68 to open this valve. The opening of valve 68 vents any accumulated gases from the interior of centrifugal pump 16 so that the pump can continue to operate to transfer liquid. While controller 61 can actuate valve 68 directly, the auxiliary control is desirable to provide an immediate opening of the valve whenever the liquid level exceeds a preselected value. Pilot valve 65 can be snap acting to provide thi result. Valve 68 is provided with a bleed, not shown, to vent air after valve 65 is closed.

In order to explain the control system of this invention in greater detail, the following example is presented which is illustrative of the operation of the absorber system.

Natural gas is fed to both absorbers where it is contacted with an absorption oil having typical properties as follows: API gravity of 42.0, viscosity of 2.4 cp. at 60 F., specific gravity of 0.816 at 60 F., and average molecular weight of 199. Absorbers 10 and 11 are operated at pressures of about 50 p.s.i.g. and 300 p.s.i.g., respectively. Typical gas flows through conduits 12, 21 and 28 are 58,000,000, 45,000,000 and 3,277,000 standard cubic feet per day, respectively. Typical oil flows through conduits 14, 15 and 22 are 742,000, 3,277,000 and 742,000 gallons per day. Approximately 2,405,000 gallons per day of oil is returned through conduit 13 from conduit 37, with approximately one-fifth of this total flow normally passing through conduit 58.

Level controller 61 can be a conventional instrument which provides an output pneumatic pressure in the range of 3 to 15 pounds, for example. This pressure increases as the level rises in absorber 10. Valve begins to open at 3 pounds pressure, and is fully open at 9 pounds pressure. Valve 62 begins to open at 9 pounds pressure, and is fully open at 15 pounds pressure. Valve 65 opens at 11 pounds pressure to apply pressure from conduit 66 to valve 68 to open the latter fully.

While this invention has been described in conjunction with a presently preferred embodiment, it obviously is not limited thereto.

What is claimed is:

1. Apparatus for removing liquid from a vessel comprising:

a vessel to contain liquid;

a centrifugal pump which includes a housing containing a liquid pumping chamber having an inlet and an outlet spaced from one another, and an impeller positioned within said liquid pumping chamber, said impeller constructed and arranged to pass liquid from said inlet to said outlet, said housing having a vent opening which fluidly communicates between said liquid pumping chamber and the exterior of said housing to permit vapor to be withdrawn from the interior of said pumping chamber;

first conduit means constructed and arranged to fluidly communicate between the lower region of said vessel and said inlet of said liquid pumping chamber;

second conduit means constructed and arranged to fluidly communicate with said vent opening in said pump housing to remove vapor which may accumulate within said liquid pumping chamber;

a valve in said second conduit means;

means to detect the liquid level in said vessel; and

means responsive to said means to detect, said responsive means opening said valve when the liquid level in said vessel rises above a predetermined level.

2. Apparatus for removing a liquid from a vessel comprising:

a vessel to contain liquid;

a centrifugal pump which includes a housing containing a liquid pumping chamber having an inlet and an outlet spaced from one another, and an impeller positioned within said liquid pumping chamber, said impeller constructed and arranged to pass liquid from said inlet to said outlet, said housing having a vent opening which fluidly communicates between said liquid pumping chamber and the exterior of said housing to permit vapor to be withdrawn from the interior of said pumping chamber;

first conduit means constructed and arranged to fluidly communicate between the lower region of said vessel and said inlet of said liquid pumping chamber;

second conduit means constructed and arranged to fluidly communicate with said outlet of said liquid pumping chamber;

a first valve in said second conduit means;

third conduit means constructed and arranged to fluidly communicate with the lower region of said vessel;

a second valve in said third conduit means;

fourth conduit means constructed and arranged to fluidly communicate with said vent opening in said pump housing to remove vapor which may accumulate within said liquid pumping chamber;

a third valve in said fourth conduit means;

means to detect the liquid level in said vessel;

first means responsive to said means to detect, said first responsive means controlling said first valve to tend to maintain a first predetermined liquid level in said vessel;

second means responsive to said means to detect, said second responsive means opening said second valve when the liquid level in said vessel rises above a first predetermined level; and

third means responsive to said means to detect, said third responsive means opening said third valve when the liquid level in said vessel rises above a first predetermined level.

References Cited by the Examiner UNITED STATES PATENTS 1,289,429 12/ 1-918 Foote. 1,437,101 11/1922 Garner et a1. 1,890,125 12/1932 Moore. 1,929,232 10/ 1933 Adams. 2,029,765 2/ 1936 Durdin 137-394 X 2,216,542 10/ 1940 Paige. 2,317,091 4/1943 Adams 137398 X 2,573,172 10/1951 Ennis et al. 2,596,692 5/1952 Jordan 5593 X 2,627,366 2/ 1953 Glick. 2,689,624 9/1954 Davis 5593 X 2,849,371 8/1958 Gilmore 5593 X 2,924,234 2/1-960 Wilson 137-392 2,998,096 8/1961 Snipes 55156 3,050,008 8/1962 Pacey et al 55168 X FOREIGN PATENTS 510,713 10/1930 Germany.

6,891 6/ 1913 Great Britain.

REUBEN FRIEDMAN, Primary Examiner. 

2. APPARATUS FOR REMOVING A LIQUID FROM A VESSEL COMPRISING: A VESSEL TO CONTAIN LIQUID; A CENTRIFUGAL PUMP WHICH INCLUDES A HOUSING CONTAINING A LIQUID PUMPING CHAMBER HAVING AN INLET AND AN OUTLET SPACED FROM ONE ANOTHER, AND AN IMPELLER POSITIONED WITHIN SAID LIQUID PUMPING CHAMBER, SAID IMPELLER CONSTRUCTED AND ARRANGED TO PASS LIQUID FROM SAID INLET TO SAID OUTLET, SAID HOUSING HAVING A VENT OPENING WHICH FLUIDLY COMMUNICATES BETWEEN SAID LIQUID PUMPING CHAMBER AND THE EXTERIOR OF SAID HOUSING TO PERMIT VAPOR TO BE WITHDRAWN FROM THE INTERIOR OF SAID PUMPING CHAMBER; FIRST CONDUIT MEANS CONSTRUCTED AND ARRANGED TO FLUIDLY COMMUNICATE BETWEEN THE LOWER REGION OF SAID VESSEL AND SAID INLET OF SAID LIQUID PUMPING CHAMBER; SECOND CONDUIT MEANS CONSTRUCTED AND ARRANGED TO FLUIDLY COMMUNICATE WITH SAID OUTLET OF SAID LIQUID PUMPING CHAMBER; A FIRST VALVE IN SAID SECOND CONDUIT MEANS; THIRD CONDUIT MEANS CONSTRUCTED AND ARRANGED TO FLUIDLY COMMUNICATE WITH THE LOWER REGION OF SAID VESSEL; A SECOND VALVE IN SAID THIRD CONDUIT MEANS; FOURTH CONDUIT MEANS CONSTRUCTED AND ARRANGED TO FLUIDLY COMMUNICATE WITH SAID VENT OPENING IN SAID PUMP HOUSING TO REMOVE VAPOR WHICH MAY ACCUMULATE WITHIN SAID LIQUID PUMPING CHAMBER; A THIRD VALVE IN SAID FOURTH CONDUIT MEANS; MEANS TO DETECT THE LIQUID LEVEL IN SAID VESSEL; FIRST MEANS RESPONSIVE TO SAID MEANS TO DETECT, SAID FIRST RESPONSIVE TO SAID MEANS TO DETECT, SAID TEND TO MAINTAIN A FIRST PREDETERMINED LIQUID LEVEL IN SAID VESSEL; SECOND MEANS RESPONSIVE TO SAID MEANS TO DETECT, SAID SECOND RESPONSIVE MEANS OPENING SAID SECOND VALVE WHEN THE LIQUID LEVEL IN SAID VESSEL RISES ABOVE A FIRST PREDETERMINED LEVEL; AND THIRD MEANS RESPONSIVE TO SAID MEANS TO DETECT, SAID THIRD RESPONSIVE MEANS OPENING SAID THIRD VALVE WHEN THE LIQUID LEVEL IN SAID VESSEL RISES ABOVE A FIRST PREDETERMINED LEVEL. 